What Is a Longitudinal Study?

When it comes to conducting surveys, generally you’ll be looking to get a snapshot view of the feelings of a group of people at single point in time.

However, there will be times when a one-off survey is not sufficient, as what you’re really interested in is getting to know how behaviours or attitudes change over time. In this situation, you’ll want to repeat your survey with the same group to see how things have changed, which is where the use of a longitudinal study or longitudinal survey can be hugely valuable.

Types of longitudinal studies

There are currently three main types of longitudinal studies.

Panel study

A panel survey typically involves studying a cross-section of individuals on broad issues and is conducted at specified intervals across an extended period of time.

An essential feature of the panel study is for researchers to collect data from the same sample at different points in time. Most panel studies are designed for quantitative analysis, although they may also be used to gather qualitative data and analysis.

Cohort Study

With a cohort study, the focus of the research is a specific cohort (essentially a group of people who typically share the same characteristics or experience the same event at a given point in time).

Surveys of this cohort will then be carried out at various intervals, often over many years to study the data and see what factors may affect the outcomes and achievements of different individuals within that group. An example of this is the UK birth cohorts, which follow groups of people born around the same time, revisiting them with surveys at various stages throughout their life to see how their lives are changing.

Retrospective study

Finally, the retrospective study looks to the past to get answers, by using already available data, collected during previously conducted research with similar methodology and variables.

This type of research is particularly popular in the medical field in trying to ascertain the risk factors involved in why some patients develop certain conditions compared with others.

To conduct a retrospective study, a researcher will typically use a mix of resources including an administrative database, pre-existing medical records, one-to-one interviews and surveys.

Advantages and disadvantages of longitudinal studies

As we’ve already discussed, longitudinal studies can be useful in a lot of different situations.

Being able to gain a unique and detailed insight of the subjects or audience under review is one of the biggest benefits of longitudinal surveys. However, here’s a wider set of advantages to consider.

The benefits of a longitudinal study

Enhanced data validation

For any long-term study to be successful, the objectives and rules for it need to be established right from the start. And because it’s a long-term study, its authenticity is typically verified in advance, which gives the results a high level of validity.

Help identify trends

Whatever you’re using it for, the long-term nature of a longitudinal study enables you to identify trends and relationships within your data, as it’s collected in real time.

The previous data can also be applied to help predict future results.

Greater accuracy when observing changes

Thanks to its reputation for being the most effective method for conducting research on development trends and making the observation of changes more accurate, longitudinal studies are seen as the number one option in a wide range of fields.

For example, in the field of marketing, longitudinal surveys can be used to measure the impact of long-term advertising campaigns on the behaviour of consumers who have seen them.

They’re really flexible

In contrast, to other research approaches, longitudinal studies offer much greater flexibility. This is because even if it has been created to study a specific data point, if unforeseen patterns or relationships appear in the data collected, the focus of the study can be shifted to accommodate this.

The drawbacks of a longitudinal study

As with any approach, there are some drawbacks that you need to be aware of with longitudinal research.

However, knowing this will help you to better assess each project on a case-by-case basis, then decide whether the benefits outweigh the costs, before moving ahead with a longitudinal research project.

They can be very time consuming

The biggest disadvantage of longitudinal studies is the length of time they take to carry out and collect results.

For some research it could take many years before the data begins to produce any observable patterns or relationships that can be monitored.

They can be costly

Without a doubt, the longitudinal survey is more complex and expensive.

This is not hard to appreciate when you consider that it’s a long-term form of research, which requires repeatedly observing and surveying the same subjects. It’s also something that can span years or decades, compared to other forms of research that can be completed in a much smaller time frame.

They often require large samples

To help develop relationships or patterns, a large amount of data must be collected and extracted to generate results. However, the trouble with this is that it can further exacerbate the time length and cost of a study.

Participation drops outs may harm your research validity

The problem with any study that is conducted over a long period of time is that for a range of reasons participants can suddenly drop out of a survey. Not only does this shrink the original size of your sample, but also the amount of data that you’re able to collect.

With the final group often looking a lot different from what it did originally, this can cause real problems for the validity of your research.

Concluding thoughts

Having explored longitudinal research, its benefits and the types of surveys that you can run alongside it, we hope you’re now better informed about how and where to conduct it.

While many surveys are still conducted to get a snapshot of a single period of time, others need to be repeated in order keep track of and maintain good relationships with stakeholders, which is where the use of longitudinal research is hugely beneficial.